The present invention relates generally to multi-layered structures or laminates and methods for manufacturing the multi-layered structures. In particular, the present invention relates to multi-layered structures having a shielding layer for blocking transmission of electromagnetic interference.
All electronic products emit electromagnetic radiation, generally in the range of 50 MHz to 1 GHz, but not limited to this range, especially considering the recent advances in high-speed microprocessor design and the rapidly increasing capabilities of high-speed networking and switching. The problem of emittance of electromagnetic radiation is not new to designers of electronic equipment; indeed, significant efforts are taken to reduce electromagnetic interference, electrostatic discharge, radiofrequency interference (hereinafter referred to collectively as xe2x80x9cEMIxe2x80x9d) and virtually every county has a regulating agency (FCC in the U.S., for instance) that restricts the marketing and sale of electronic equipment that do not pass stringent requirements for EMI, whether radiation or intercepted (also called susceptibility) by an electronic device.
Present day solutions for EMI shielding generally include the use of conductively painted plastic housings, conductive gaskets, and metal cans that are affixed to the printed circuit board by soldering or similar methods, some of which are semi-permanent. In virtually all cases, however, the existing solutions are expensive and add to the cost of providing electronic equipment such as cell phones, personal digital assistants, laptop computers, set-top boxes, cable modems, networking equipment including switches, bridges, and cross-connects.
In an effort to bring costs down while increasing shielding, various technologies for the metallization of polymer substrates has been developed. For example, U.S. Pat. No. 5,028,490 to Koskenmaki describes layering a polymer substrate with aluminum fibers and sintered to form a flat material with a metal coating that is intended to provide effective EMI control (also called electromagnetic control or EMC). In actual use, however, the material has been shown to be expensive, difficult to use, and subject to inferior performance due to cracking of the metallized layer. Unfortunately, the metal-layered material has not been able to withstand a thermoformed process due to the typical tight radius used in the thermoforming molds.
U.S. Pat. No. 5,811,050 to Gabower, the complete disclosure of which is incorporated herein by reference, has provided an alternative approach wherein the thermoformable substrate (any number of polymers) is first formed and then metallized. This approach offers the advantage of eliminating the stresses to metallized layer created during molding. The product has been shown to be highly effective and relatively low-cost.
Plastic housings, because they are not conductive, provide no shielding of electromagnetic radiation. Attempts to provide plastic with a conductive feature include intrinsically conductive plastics and plastics loaded with conductive fillers (carbon or nickel flakes, for instance). Generally, these plastics are prohibitively expensive, or at least not economically feasible given alternative technologies (cans, gaskets, and conductive painting). Additionally, the level of shielding effectiveness is also small, typically less than 40 dB, whereas the demands of many computing devices, both mobile and fixed, require shielding effectiveness greater than 40 dB.
Historically, metals have been used for housings of fixed location equipment and electronic devices. Fixed electronics, such as personal computers, printers, fax machines, etc. are typically contained in metal housings or, if plastic housings are used, the printed circuit boards (PCBs) are shielded in some manner (cans, for instance on selected high-emission components and traces). Mobile devices often used plastic housings and some combination of conductive gaskets, metal cans, and conductive painting of the housing to achieve the desired shielding effectiveness. As the frequency of emissions increases as a result of smaller components, circuits, and the closer locating of analog/digital circuits, the need for shielding increases and the need for greater shielding effectiveness also increases. The drive to create smaller, lighter mobile products also creates a need for lighter and thinner shielding solutions.
Recently, the use of in-mold and insert-mold plastic molding processes have become of great interest to the electronics packaging industry. With in-mold processes, a relatively thin material is drawn into or placed into a plastic injection mold and used as a xe2x80x9cdamxe2x80x9d or backstop for the injection plastic material that typically becomes the structural housing. Such processes provide some interesting design features for a variety of products.
While the in-mold processes have been effective in creating decorative housings, the current in-mold processes, however, do nothing to solve the difficult issue of EMI shielding.
The present invention provides multi-layered inserts, laminates, housings, and electronic devices that have a metal layer that provides improved decorative features and/or EMI shielding.
In exemplary uses, the multi-layered structures of the present invention can be used to create housings and electronic devices that have an EMI shield integrated with the housing. The housings of the present invention can provide shielding of greater than 40 dB for radiation in the range of 50 MHz to 1 GHz, or more. In addition to providing EMI shielding, the metal layers of the present invention can also provide a decorative layer, such as a xe2x80x9cmetallic lookxe2x80x9d or a reflective surface. The integrated plastic/shielding housing can be used for both fixed and mobile electronic products.
In general, the electronic devices of the present invention include a housing having film layer, at least one metal layer having a thickness that is sufficient to block the transmission of EMI, and a resin layer. The electronic devices typically include a printed circuit board disposed within the shielded housing in which the EMI shield layer is grounded.
The film layers incorporated into the structures of the present invention will typically be shaped to a desired form prior to the deposition of the resin onto the film. In exemplary embodiments, the film layer is a thermoform that is shaped using conventional thermoforming techniques (e.g., vacuum, pressure, or mechanical forces). It should be appreciated however, that the film layer can be shaped using any conventional or proprietary methods.
The metal layers of the present invention are also typically attached to the film layer after shaping of the film layer. If the metal layer is applied prior to shaping of the film layer, the shaping process (e.g., thermoforming) tends to stretch out and weaken portions of the metal layer. Such stretching and thinning has been found to weaken and sometimes destroy the EMI capabilities of the metal layer. The EMI shields of the present invention will generally have a substantially even thickness that is sufficient to block the passage of EMI. Typically, the metal layer will have a thickness between approximately 1 microns and 50 microns. In such embodiments, the metal layer will typically be grounded so as to create a Faraday cage.
Typically, the metal film layer is deposited onto the film layer using vacuum metallization. Vacuum metallization is one preferred method because of the substantially even layer of metal that can be applied to the shaped film to create the EMI shield. It should be appreciated however, that other methods of depositing the metal layer to the substrate can be used without departing from the scope of the present invention. For example, instead of vacuum metallization, other methods such as a depositing a random mat or fiber weave, sputtering, painting, electroplating, deposition coating, electroless plating, laminated conductive layers, or the like, can be used to deposit the metal layer onto the multi-layered laminate.
It should be appreciated that, in addition to EMI shielding, the metal layers of the present invention can be also used for decorative purposes or reflective purposes. Such metal layers are typically composed of materials such as aluminum and its alloys, copper and its alloys, tin and its alloys, silver and its alloys, nickel and its alloys, or the like. Additionally, instead of a single layer, it is possible to apply two or more layers using the same or different materials. For example, in some embodiments it may be possible to apply a nickel layer and a tin layer over the polymer film layer. In one preferred embodiment, an aluminum metal layer created by vacuum metallization has a luster and reflective properties similar to that of chrome. Such a metal layer is beneficial, particularly when the metal layer is used as a reflector.
Depending on the combination of materials and the sequence of deposition, the multi-layered structure may need a protective undercoat to improve adhesion between layers or an overcoat to protect the top layer of the laminate. Thus, as used herein, xe2x80x9ccoupling two layersxe2x80x9d or xe2x80x9cattaching two layersxe2x80x9d are meant to encompass both directly and indirectly (e.g., another layer in between the two layers) bonding the two layers together.
The present further includes shielded/decorated inserts for an in-mold and insert-mold processes. Multi-layered inserts of the present invention for the in-mold manufacturing process includes a shaped substrate (such as a thermoform) having a decorative feature disposed along at least one surface. A metallized layer can be disposed over at least one of the substrate and decorative feature.
Methods of in-mold and insert mold shielding of the present invention include forming a multi-layered laminate for use in an in-mold process. A decorative feature can be applied to at least one surface of a substrate. The decorated substrate is then shaped into a desired shape. A metal layer is then deposited onto at least one surface of the decorated and shaped substrate.
After the multi-layered insert is manufactured (either locally or remotely), the shaped metallized substrate can be manually or robotically placed into an injection molding chamber and an injection molding resin can be deposited on the metallized substrate. The resulting multi-layered laminate from the in-mold process provides a pre-shaped film having a metal layer coupled thereto, and an injection molded plastic structured coupled to either the film or the metal layer.
In exemplary embodiments, the metal layer coupled to the substrate has a thickness that is sufficient to act as an EMI shield. Thus, if the shaped substrate is formed into a housing for an electronic device, the electronic device will have a conformal EMI shield integrated into its housing. Optionally, the multi-layered structure can include a second metal layer. The second metal layer can be decorative in nature or for aesthetic purposes.
One or both of the first and second metal layer can be used to create a bright, reflective, and shiny surface to provide a design element. With the second metal layer containing a decorative image on a first side of the substrate and EMI shielding on a second side of the substrate, a highly effective and aesthetically designed electronics product can be produced.
In another aspect, the present invention provides structures and methods for grounding a metallized layer, such as a shielded electronic housing with a ground trace of a printed circuit board. In exemplary embodiments, the grounding methods comprises placing a solder paste over ribbed portions of the electronic housing to mechanically and conductively contact the ground traces on the printed circuit board. In another exemplary embodiment, the present invention creates a via or perforation in the electronic shield and deposit a conductive adhesive or molten solder to create a mechanical and conductive bond between the metal layer on the shield and the ground trace. Other methods include soldering, ultrasonic welding, conductive adhesives, laser melting, and the like.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.